UCSF

Accurate localization of epilepsy foci is essential prior to resection of epileptogenic zones of the brain. EEG signatures indicative of epileptic seizures can be mapped to their location on a brain MRI by acquiring the MRI before implanting the electrodes in the brain, and localizing the electrodes within the head with a CT after implantation. However, distortion resulting from the craniotomy and the implantation procedure change the brain geometry causing the frame of reference to shift and this model to be inaccurate. Using B-Spline transformations and an Advanced Mattes Mutual Information metric, a nonrigid registration was performed between CT scans before and after the implantation procedure. This transformation was subsequently applied to the MRI in order to correct for the mismatch in registration in 5 subjects. After the application of this nonrigid transformation there was an average increase in accuracy of 12.5% ± 2.3% (p<0.001) in the ability of depth electrodes to localize gray matter. On average, the grid electrodes were 3mm ± 3mm (p= 0.06) closer to their locations given by an intraoperative photograph in one patient when the transformation was applied as well. This has been incorporated into a completely automated tool that can be easily implemented into a lab or clinical environment.